1. Field of the Invention
The present invention relates to an image forming apparatus using xerography such as a printer, a copy machine, a facsimile machine, a multifunction peripheral provided with functions thereof and the like, and particularly to an image forming apparatus provided with a discharging unit for eliminating electrical charge on a surface of a photoreceptor drum.
2. Related Art
Conventionally, an image forming apparatus using xerography has been known that prints an image by forming an electrostatic latent image on a surface of a photoreceptor drum, developing the electrostatic latent image by a toner, and then transferring a toner image to paper and the like. As such an image forming apparatus using xerography, an image forming apparatus as shown in FIG. 10A including: a photoreceptor drum 81 disposed along a paper path 80 of transfer paper; a charging unit 82 that charges a surface of the photoreceptor drum 81 at a predetermined voltage; an exposure unit (not illustrated) that forms an electrostatic latent image by irradiating the surface of the photoreceptor drum with a laser beam P; a developing unit 83 that develops the electrostatic latent image formed by the exposure unit as a toner image on the surface of the photoreceptor drum; a transfer roller 84 that transfers the toner image to the transfer paper in cooperation with the photoreceptor drum 81; a cleaning unit (a cleaning roller 85 and a cleaning blade 86) that removes the toner remaining on the surface of the photoreceptor drum 81 after transfer; and a discharging unit 87 including a light emitting body 88 that emits discharging light for eliminating electrical charge remaining on the surface of the photoreceptor drum after transfer has been known. Note that, in FIGS. 10A and 10B, an arrow shown inside each component shows a rotational direction of the component, and an arrow shown along the paper path 80 of the transfer paper shows a feeding direction of the transfer paper.
In such an image forming apparatus, subsequent charging is performed preferably after sufficiently removing electrical charge from the surface of the photoreceptor drum 81 by the discharging unit 87. However, in a prior art shown in FIG. 10A, since the discharging unit 87 is disposed immediately before the charging unit 82 in a rotational direction of the photoreceptor drum 81, a rotational angle α between a discharging position and a charging position is small and a time interval between discharging and charging is short. Accordingly, if the photoreceptor drum 81 rotates in high speed as a result of increase in processing speed of the image forming apparatus, subsequent charging is started before sufficiently discharging the surface of the photoreceptor drum 81, easily causing an image defect.
Given this, an image forming apparatus as shown in FIG. 10B in which the discharging unit 87 is disposed more on an upstream side in a rotational direction of the photoreceptor drum 81 than the cleaning roller 85 and the cleaning blade 86 has been known. In such a configuration, the cleaning roller 85 and the cleaning blade 86 are disposed between the discharging unit 87 and the charging unit 82, thereby keeping the charging unit 82 away from the discharging unit 87. As a result, the rotational angle α between the discharging position and the charging position can be made greater than in a case of FIG. 10A and a time interval between discharging and charging can be made longer. This can prevent a problem of subsequent charging being started before sufficiently discharging the photoreceptor drum 81.
However, as shown in FIG. 10B, in a case in which the discharging unit 87 is disposed more on the upstream side in the rotational direction of the photoreceptor drum 81 than the cleaning roller 85 and the cleaning blade 86, the discharging unit 87 is disposed close to the paper path 80 of the transfer paper. Generally, in the vicinity of the paper path 80, matters such as paper dust and unfixed toner generated in paper feeding, as well as residual toner remaining on the surface of the photoreceptor drum 81 after transfer, are scattered. Accordingly, if the discharging unit 87 is disposed in the vicinity of the paper path 80, a surface of the light emitting body 88 fixed to the discharging unit 87 is contaminated with the abovementioned scattered matters, thereby reducing intensity of discharging light emitted from the light emitting body 88. As a result, it is difficult for the discharging unit 87 to exert an original discharging ability and an image defect may be caused.
Given this, a configuration in which the surface of the light emitting body 88 is cleaned by a cleaning member and a configuration in which the surface of the light emitting body 88 is covered with dustproof glass or the like have been known.
However, by employing the configuration in which the cleaning member for cleaning the surface of the light emitting body is provided and the configuration in which the surface of the light emitting body is covered with dustproof glass or the like, a new problem of increased number and cost of components arises.